The present invention relates generally to radio frequency (RF) signal filters, and more particularly to a single-block filter for antenna duplexing and antenna-switched diversity in duplex radio transceivers.
A prior art single-block ceramic filter for antenna duplexing is shown and described in U.S. Pat. No. 4,742,562. However, such prior art single-block ceramic filter does not accommodate antenna-switched diversity.
In the past, antenna-switched diversity has been used to minimize the effects of signal fading in mobile radio communications systems, a problem which is aggravated in cellular telephone systems due to operating frequencies above 800 MHz. According to a prior antenna-switched diversity scheme, a receiver is switched between a first antenna and a second antenna in response to detection of degradation in the received signal. This has been accomplished in prior art cellular telephones by utilizing a transmit filter and two separate receive filters and switching the input of the cellular telephone receiver between the two receive filters, or by using a transmit filter and a receive filter and switching the input of the receive filter between the two antennas. However, in both of the foregoing instances two separate filters are required.